In order to optimize spectacle lenses, in particular customized progressive lenses, it is known to take account of various parameters of the eye/spectacles system. These parameters are, for example, the pupil distance PD, the corneal vertex distance HSA, the forward inclination angle α of the spectacle lens, the frame disk angle (αR, αL) for the right-hand and left-hand spectacle lens, as well as the location of the optical or mechanical ocular pivot point (Z′, M). Customized progressive lenses are understood to be progressive lenses in the case of which at least one individual use parameter is taken into account when calculating the spectacle lens, and which are fabricated by means of free-form technology, as this is described, for example, in the Deutsche Optikerzeitung DOZ 4+5/2000 by W. Grimm and G. Kelch in the article “Gradal® Individual: Konzeption, Fertigung and Anpassung”, [Gradal® Customized: design, fabrication and adjustment”], in U.S. Pat. 6,089,713 and/or in U.S. Pat. No. 5,444,503.
In the case of non-customized spectacle lenses, these parameters are determined from statistical mean values of a representative cross section of the population. By contrast, in the case of customized spectacle lenses the parameters are measured individually on the respective spectacle wearer, for example, with the aid of so-called video centering systems such as are produced and marketed by Carl Zeiss Vision GmbH of Aalen, Germany, under the product designations of “i.Terminal” and “Relaxed Vision Terminal”. However, these video centering systems are so far not in a position to be able to optimize the spectacle lens with the aid of the location of the ocular pivot point in a sufficiently exact way.
If it is desired to take account of the location of the ocular pivot point, the location can be derived in a known way from the eye length via the mean sphere of the prescribed spectacle lens. However, in this case many assumptions are made that do not sufficiently correspond to the actual circumstances.
The relationship between eye length and the sphere of the prescribed spectacle lens is frequently assumed for simplicity as being linear. However, this is not the case in reality, because both the curvature of the cornea and the eye lens as well as the eye length increase very independently of one another and/or develop differently.
It is sufficient in general to regard the ocular pivot point as a point pivot center inside the eye. However, the invention also comprises in very general terms an extended, generally approximately spherical, ocular pivot point zone. For the sake of simplicity, unless otherwise mentioned, a point ocular pivot point is the starting point below for describing the invention and the prior art.
The usual procedure for prescribing spectacles is for the spectacle lenses to be prescribed and centered on the basis of a subjective refraction and a video centering measurement.
It is disadvantageous in this that there is no referencing between the determination of refraction and the centering, because the two operations are carried out by different apparatus. For example, when the refraction is determined with the aid of a phoropter, it can happen that the phoropter is tilted by a first angle relative to the line that connects the two pupil centers of the eye. Furthermore, it can happen that the selected spectacle frame is rotated relative to this line by a second angle. In the most unfavorable case, the two angles can add up, and this can lead to a discrepancy of a plurality of angular degrees in the axes of the cylinders between the prescription and the correction done on the finished spectacles.
U.S. Pat. No. 7,794,085 discloses a method and an apparatus for determining the location of the ocular pivot point. In the case of this known method, a test person looks into a unit resembling a telescope. The alignment of the unit in space is determined by a three-dimensionally active sensor located on the unit. The test person wears on his head a further such sensor, which determines the position and alignment of his head. Located in the unit on the side averted from the test person is a light source that emits a light ray along an optical axis. Located between the light source and the eye of the test person are two gratings with central marks. The test person now moves the unit until the light ray and the two marks coincide. The position of the viewing axis in space is calculated from the position data found in this case for the unit and the head. The operation is then repeated several times from different viewing directions so that a plurality of viewing axes are determined. The pivot point is then calculated as the location of the ocular pivot point.
This known procedure has the disadvantages that there is a need for a substantial outlay on separate units. Furthermore, the measuring accuracy depends on the subjective behavior of the test person.
U.S. Pat. No. 6,580,448 discloses a method and an apparatus for acquiring visual information in parallel. In a fixed alignment and position of the head of the test person, in order to determine the location of the ocular pivot point in the case of this known procedure the fixation line is determined for at least two known fixation points fixated successively by the eyes. The fixation points are two marking points that can be permanently connected to the holder of cameras and sensors in order to determine the pupil position. The ocular pivot point then lies at the intersection of the fixation lines defined by the fixation points.